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Describing the Geomorphological History of the Fourth of July Cirque in the Front Range, Colorado by Using Soil Dating, Lichenometry and Rock Weathering

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Describing the Geomorphological History of the Fourth of July Cirque in the Front Range, Colorado by Using Soil Dating, Lichenometry and Rock Weathering Describing the geomorphological history of the Fourth of July cirque in the Front Range, Colorado by using soil dating, lichenometry and rock weathering Name: Martijn Schwering Student number: 890307756130 Supervisor: dr.ir. AJAM (Arnaud) Temme 1 Abstract A better understanding of the reactions of glaciers to climatic changes can be used to calibrate climatic models and improve these models so that predictions about the distribution of climatic conditions in the future will be more accurate. In the Fourth of July cirque multiple glaciations have taken place during the last 30 000 years. The deposits in the study area range from glacial deposits, such as moraines, to slope landforms, such as mudflows and ramparts. The age and responsible process of deposition of some of the landforms are still under discussion in literature, this study resolves some of these issues. The geomorphological history of the Fourth of July cirque was described with the use of field reconstruction, soil dating, lichenometry and rock weathering. These three different relative dating methods were used because they are cheaper, easier and less time consuming than absolute dating techniques, such as cosmogenic radionuclide exposure dating, are. It has been investigated to which extent each of these methods can be used to describe the evolution of a landscape. Soil dating yielded relative ages for the different landforms that were in line with the field reconstruction. The amount of rock weathering unfortunately could not be used to obtain detailed relative age trends. Lichenometry could be used to some extent to differentiate landforms of different age. Most of the landforms were older than the maximum age of the lichen species used in this research though, which made this method only useful for a few younger landforms. 2 Table of contents I Introduction .............................................................................................................................. 6 Objectives ............................................................................................................................... 8 II Study area ............................................................................................................................... 9 Location .................................................................................................................................. 9 Climate ................................................................................................................................... 9 Bedrock ................................................................................................................................ 10 Glacial history ...................................................................................................................... 10 Post-glacial landscape development ..................................................................................... 11 III Materials and methods ....................................................................................................... 13 Field reconstruction .............................................................................................................. 13 Field work ............................................................................................................................ 13 Soil dating ............................................................................................................................ 14 Rock weathering ................................................................................................................... 18 Lichenometry ....................................................................................................................... 18 Materials ............................................................................................................................... 19 IV Results ................................................................................................................................. 20 Field observations ................................................................................................................ 20 Soil dating ............................................................................................................................ 27 Rock weathering ................................................................................................................... 31 Lichenometry ....................................................................................................................... 34 V Discussion ............................................................................................................................ 37 Post-glacial landscape development ..................................................................................... 37 To which extent can the soil development index be used to describe the evolution of a landscape? ............................................................................................................................ 37 To which extent can the amount of rock weathering be used to describe the evolution of a landscape? ............................................................................................................................ 42 To which extent can lichenometry be used to describe the evolution of a landscape? ........ 43 What is the geomorphological history of the landscape in this study? ................................ 46 VI Conclusion .......................................................................................................................... 47 References ................................................................................................................................ 48 Appendix I: Soil site and surface descriptions ......................................................................... 51 Appendix II: Rock site and surface descriptions and measurements ....................................... 52 Appendix III: Overview of soil characteristics, PDI and HDI values ...................................... 53 3 Table of figures Figure 1: Location of study area the Fourth of July valley. ....................................................... 9 Figure 2: The study area. ............................................................................................................ 9 Figure 3: The main rock types in the Fourth of July cirque. .................................................... 10 Figure 4: Results of Mahaney. ................................................................................................. 12 Figure 5: Results of Williams. .................................................................................................. 12 Figure 6: The Fourth of July cirque with the landforms drawn in based upon field observations only. ..................................................................................................................... 20 Figure 7: The biggest of the multiple terminal moraines present in the cirque........................ 21 Figure 8: Landforms 2, 3 and 4. ............................................................................................... 22 Figure 9: Rocks from landform 1 have fallen on top of landform 2. ....................................... 23 Figure 10: Stream patters on landform 4 are visible as little ridges (indicated with red lines) of rocks with gullies in between them. ......................................................................................... 24 Figure 11: Landforms 4, 5, 7, 8 and 9. ..................................................................................... 25 Figure 12: Locations of the soil pits. ........................................................................................ 27 Figure 13: The value of the PDI for every soil pit. .................................................................. 28 Figure 14: The value of the Development Index for every Bw horizon. ................................. 29 Figure 15: pH difference between the Bw horizon and the C horizon (pH_C - pH_Bw). ....... 30 Figure 16: Map with all the locations of the rocks that were measured. .................................. 31 Figure 17: Average rebound values for the last 20 rocks that were measured. ........................ 32 Figure 18: Age according to (Benedict, 1967) of the biggest R.Geographicum lichen thallus per rock. .................................................................................................................................... 34 Figure 19: Lichen cover (in %) per rock. ................................................................................. 36 Figure 20: Maximum diameter R.Geographicum thalli measured on 50 moraines in the Indian Peaks area. The measurements fall into three broad size classes, suggesting three major periods of Little Ice Age glaciation .......................................................................................... 44 4 Table of tables Table 1: Assumptions for values of soil properties of the parent material............................... 16 Table 2: Materials used for the field work. .............................................................................. 19 Table 3: The PDI for every soil pit........................................................................................... 28 Table 4: Average, maximum and median rebound values per landform. ................................ 33 Table 5: Ages of the biggest R.Geographicum thalli for multiple
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